1. Field of the Invention
The present invention relates to a light diffuser mechanism, and more particularly to an adjustable light diffuser mechanism used in an optical, or image scanner.
2. Description of the Related Art
Conventional image or optical scanners employ a light source which emits light to be projected (i) on a scanned object so that the light is reflected from the scanned object or (ii) transmitted through the scanned object. The reflected or transmitted light then passes through a conventional lens and from there to a charge coupled device (CCD) which in turn transforms the light into a series of electrical signals. Those signals are then processed and ultimately converted into an image output typically displayed on a screen, or printed by a printer.
There are numerous disadvantages associated with conventional light sources for scanners, which disadvantages include:
a. Conventional light sources tend to darken in light intensity from use over time, such as conventional fluorescent light bulbs which darken due to deterioration of the phosphor coating surrounding the interior surface of the bulb that glows in reaction to exposure from ultraviolet radiation. A conventional light source typically cannot be adjusted to compensate for such changes in light intensity, due in part to the fact that the changes do not occur uniformly throughout the light source. The inability to compensate for changes in the light intensity can be compounded where it may be desirable in some scanner applications to adjust the illuminance of scanned objects in order to achieve a desired visual effect. The term "illuminance" being defined as the light intensity per unit area on an intercepting surface at any given point, where "light intensity" is used synonymously with "luminous flux." Therefore, the number of applications available for scanners using a conventional light source can be limited by the various changes in light intensity experienced over time.
b. In scanners operating in a transmission mode, that is, where the light source is projected through the scanned object, such as a film or transparency, overexposure is sometimes a problem. When the light source emits a light of too great an intensity, the corresponding electrical charge measured by the CCD exceeds the operational range of the CCD resulting in saturation. Once the CCD experiences saturation due to overexposure, the sensitivity of the CCD is affected and then is not able to produce accurate electrical signals to identify the various color and intensity characteristics of the light coming from the scanned object. This problem is analogous to the problem of photographic film being overexposed because too much light is allowed the pass through the camera lens to the film and, consequently, overexposure produces a finished transparency or picture in which the various colors and intensity of colors on the image are washed out or obliterated. The aforementioned overexposure problem can be overcome by known methods which include (i) increasing the distance between the light source and the scanned object and/or (ii) using a light source having a reduced light intensity. However, these methods are impractical or not economical for several reasons. First, the scanner has a certain, limited size. Therefore, increasing or decreasing the distance between the light source and the scanned object is, for a given scanner design, impractical or impossible. Second, although a voltage regulator, operating as a dimmer, could be used to reduce the voltage across the lamp thereby reducing the intensity of light generated, the inclusion of a voltage regulator in a scanner would increase the number of electrical components and production costs of a scanner, without providing corresponding value in adjustability.
c. Conventional scanners typically use a long, cylindrical fluorescent lamp which projects light waves radially away from the lengthwise axis of the lamp. The light waves, intercepting the scanned object, eventually travel through a lens and finally intercept the CCD. Those skilled in the art will appreciate that the light waves traveling the shortest distance from the lamp to the CCD may have an appreciably greater light intensity than the light waves travelling the farthest distance from the lamp to the CCD. For scanner configurations where the lens and CCD are all centered with respect to the mid-point of the lengthwise axis of the florescent lamp, the light waves generated at the lengthwise ends of the florescent lamp travel the greatest distance through the lens to the CCD and therefore have a relatively weaker light intensity upon intercepting the CCD. The problem is that the CCD's optimum exposure time for recording light waves from the scanned object is not uniform and is greater for light waves traveling from the ends of the florescent lamp.
d. In conventional scanner designs, the distances the light waves travel from the light source to the CCD, the size of the lens, and the sensitivity of the CCD may vary depending upon the intended application of the scanner. It will be appreciated by those skilled in the art that such configuration variations can compound the problems associated with the illuminance of the scanned object as recorded by the CCD.